"The standard disk partition format on an Intel-based Macintosh computer differs from the disk partition format of a PowerPC-based Macintosh computer. By default, internal hard drives on Intel-based Macintosh computers use the GUID Partition Table (GPT) scheme and external drives use the Apple Partition Map (APM) partition scheme. To create an external USB or FireWire disk that can boot an Intel-based Macintosh computer, select the GPT disk partition scheme option using Apple Disk Utility."